A launch pad is the area and facilities where rockets or spacecrafts liftoff. A typical launch pad consists of the service and umbilical structures. The service structure provides an access platform to inspect the launch vehicle prior to launch. Most service structures can be moved or rotated to a safe distance. The umbilical structure has propellent loading, gas, power, and communication links to the launch vehicle. The launch vehicle sits atop of the launch platform, which has the flame deflection structure to withstand the intense heat and load generated by rocket engines during liftoff.
Most cryogenic launch vehicles need to be continuously topped off as scheduled liftoff approaches. This is particularly necessary as various holds are placed on the liftoff and then removed as support personnel correct problems or verify they are not serious. Without the ability to top off the launch vehicle, the launch would have to be scrubbed when problems slowed down the countdown. Gantries are commonly designed and constructed on launch pads to meet these types of servicing requirements both during launch and in the preparation period leading up to it.
Most rockets need stable support for a few seconds after ignition while the engines ramp up and stabilize at full thrust. This stability requirement is commonly met by the use of explosive bolts to connect the launch vehicle to the pad. When the vehicle is stable and ready to fly the bolts explode, severing the vehicle's ties to the launch pad and structures on the ground.
There are several different types of launch site, determined by the means by which the rocket gets to the pad.
- The first large rocket, the V-2, travelled horizontally with its tail forward to the launch site at Peenemünde. This is the most common; it was used for all large Soviet rockets, even Buran.
- In a similar manner, at the Soviet launch site near Volgograd, a silo used to launch test rockets would have its top opened and a second stage and payload would be driven in horizontally and tilted on top of a first stage already in the silo, the nose cone and some of the second stage remaining visible above ground. Hence no surface pad is used; Russian silos are reusable. This method was only used for the Cosmos series of small satellite launching vehicles.
- Like the Saturn V and Saturn IB rockets launched from Launch Complex 39 at the Kennedy Space Center in the past, the Space Shuttle vehicles are first assembled vertically in the Vehicle Assembly Building on a Mobile Launcher Platform (MLP). The assembled shuttle and MLP ride on top of a Crawler-Transporter, which slowly drives to the launch pad. A similar system is used to launch Ariane 5 rockets at ELA-3 at Guiana Space Centre, a French spaceport near Kourou in French Guiana.
- At Cape Canaveral Air Force Station, two parallel standard gauge railroad tracks were used to transport the Titan launch vehicle and its mobile launcher platform from the integration building to the launch areas at Complex 40 and 41, and continue to be used for the Atlas V.
- In the 1920s, Hermann Oberth described a method in which the rocket is assembled vertically on a floating barge, which he used in the movie Frau im Mond. This has never been used, although it was seriously considered for use at Kennedy Space Center Launch Complex 39 for the Saturn V. It was rejected for that application due to the instability of the top-heavy unfuelled rocket and gantry.
- At Vandenberg Air Force Base, in California, the Titan series of rockets were set up vertically in a gantry in a windowless building at SLC-4, the outside walls of which would be rolled away just at launch. This was done for purposes of military secrecy. Similar systems are used at SLC-6 and LC37 at Cape Canaveral Air Force Station for the Delta IV rocket, ELA-1 & 2 at CSG for the Ariane 1-4, and Kagoshima for the M-V.
- Zenit 3SL rockets of Sea Launch are transported horizontally by sea aboard the Ocean Odyssey converted oil rig, which is then used to erect and launch them.
- Dnepr rockets are transported vertically and then inserted into a silo.